Besides the major flooding of main rivers, significant damage is caused by flooding of smaller tributaries. Thus flood protection measures implemented through large engineering projects must - to make them efficient as possible - be complemented by integrated river catchment management, implying the active involvement of farmers, foresters, and residents, since changing both user habits and land use will have an impact on water retention and run-off. This technical water project, led by the German Research Institute for Forest Ecology and forestry (Rheinland-Pfalz), which brings together a total of 11 partners from Germany, France, Luxembourg and Switzerland over 4½ years, looks at preventative water retention measures implemented across the NWE. The economic, ecological and managerial efficiency of different measures will be assessed by calculating their effects across different landscape structure, meteorological situations and types of land use in the Member States involved. WaReLa will use GISbased systems and open programme-controlled systems (and promote training in them) to test individual flood scenarios, compile a comprehensive overview and elaborate a regional planning framework/decision support system for transnational river basin management. The transnational network of partners consists of expertise from hydroclimatological analysts, flood experts, decision-makers, farmers and local water authorities, who will all benefit from a transfer of knowledge within the partnership. Achievements: WARELA: The project was successful in all its test and demonstrations sites. The greatest achievements were to convince stakeholders and land-users from the idea of precautionary flood mitigation measures during excursions into the demonstration areas. Effective land-use measures to retain water, wherever it was possible, were explored and implemented in the WaReLa-test-sites. With the help of a geographic information system (GIS)-based tool flood generating areas can be visualized as hot spots for run-off mitigating and delaying measures. Also the spatial flood and retention potential within the low-mountain range landscapes can be seen in GIS-maps. For this the very different land use options as well as the various landscape features were analysed by remote sensing methods. The efficiency of precautionary land-use measures to mitigate flood damages was evaluated exemplarily on a process-controlled basis at plot scale and at river basin scale, taking pedological and geological factors as well as landscape features into account. Building on this a digital tool was developed to evaluate the eco-efficiency, the economical consequences and the sustainable benefit of precautionary flood mitigating land-use measures to support the decision process. The methods and results of the WaReLa-project are integrated in an expert spatial planning system. Spatial planning is an important instrument to reconcile the various interests in a catchment area. Hence the WaReLa-project elaborates a range of transnationally applicable decision-making instruments for the spatial planning and the future land-use.